An electronic photo device such as an electronic photocopier, and an electronic photoprinter has a mechanism which uniformly charges an outer circumference of a photoconductive drum, then exposes a printing pattern or copying pattern on the outer circumference of the photoconductive drum so as to form an electrostatic latent image, deposits a toner on this electrostatic latent image to form (develop) a toner image, and transfers this toner image to copier paper or printer paper to print or copy the image.
In such an electronic photo device, as the charging roll for uniformly charging the outer circumference of the photoconductive drum, the developing roll for developing the electrostatic latent image of the outer circumference of the photoconductive drum to a toner image, the feed roll for feeding toner to the developing roll, and the transfer roll for transferring the toner image, a rubber roll is used. As such a rubber roll, usually a conductive rubber roll which is comprised of rubber to which conductivity imparting material such as carbon black is added is used.
However, while such a conductive rubber roll is improved in conductivity by addition of the conductivity imparting material, its hardness ends up becoming higher and therefore the “nip” when contacting another member can no longer be sufficiently obtained and sometimes trouble occurs in the electronic photo device.
To deal with such a problem, the method is known of blending into the conductive rubber roll a plasticizer or softener so as to cause the hardness to drop. However, there is the problem that a plasticizer or softener bleeds out to the roll circumference when applying voltage to the conductive rubber roll and thereby ends up contaminating other members, in particular, the photoconductor.
To solve the problem of contamination of the photoconductor due to such bleedout, for example, Patent Document 1 discloses a conductive rubber roll which contains a solid rubber (A) in 40 to 90 parts by weight, which is comprised of an ethylenically unsaturated nitrile monomer in 10 to 60 wt %, conjugated diene monomer in 40 to 90 wt %, and other ethylenically unsaturated monomer in 0 to 20 wt % polymerized together, a liquid rubber (B) in 10 to 60 parts by weight, which is comprised of an ethylenically unsaturated nitrile monomer in 10 to 60 wt %, conjugated diene monomer in 40 to 90 wt %, and other ethylenically unsaturated monomer in 0 to 20 wt % polymerized together, and another solid rubber (C) in 0 to 50 parts by weight. However, the conductive rubber roll which is disclosed in this Patent Document 1 is high in electrical resistance value, so is insufficient for achieving the higher speeds which are being sought from electronic photo devices in recent years.
As opposed to this, as art which lowers the electrical resistance value while solving the problem of bleedout, Patent Document 2 discloses a rubber composition for conductive rubber roll which contains a rubber component (A) in 100 parts by weight, which contains an epihalohydrin rubber (Al) which has a Mooney viscosity (ML1+4, 100° C.) of 20 to 200 in 40 to 90 wt % and a low molecular weight epihalohydrin polymer (A2) which has an ηsp/C of 0.01 to 0.5 in 60 to 10 wt %, and carbon black (B) in 10 to 250 parts by weight which has an average particle size of 90 to 560 nm and a specific surface area of 5 to 20 m2/g. However, in the art of Patent Document 2, there are the problems that so as to obtain lower the electrical resistance value, it is necessary to add a conductivity imparting material constituted by carbon black in a relatively large amount and further lowering the hardness of the obtained conductive rubber roll is difficult.